By extending the path integral framework to include two-photon entangled measurements, a wide array of intriguing entanglement phenomena becomes amenable to a path-based analysis. One of the more surprising consequences of quantum theory (apart from entanglement itself) is the case of “entanglement swapping” (ES), where two photons are said to become entangled despite never interacting with each other in the past or future [1]}. Indeed, entanglement can even be arranged to occur between two photons whose worldlines are entirely spacelike-separated from each other.
